It is now realized that the "green algae" should not be a formal taxonomic group, since they are paraphyletic with respect to the Plantae. In fact one group of "green algae", the "charophytes" is more closely related to the plants than to the other "green algae". Like plants, the "green algae" have chlorophylls "a" and "b", and an alternation of generations. Unlike the plants, however, the alternation may be isomorphic, so that the gametophyte and sporophyte are indistinguishable.
The major groups of "green algae" are distinguishable on the basis of their flagellar insertion (the number and arrangement of the flagella that the cells have); their method of cell division; and their habitat.